Re: [RFC PATCH] git-sh-setup: Use "cd" option, not /bin/pwd, for symlinked work tree

["Marcel M. Cary" <marcel@oak.homeunix.org>]

Johannes Schindelin wrote:
> On Fri, 6 Feb 2009, Marcel M. Cary wrote:
>> While the "-P" option may be slightly less commonly supported than
>> /bin/pwd,
>
> Does this not suggest that your patch should at least fall back to
> using /bin/pwd when it was detected that "cd -P" does not work?

Having the "cd -P" strategy fall back to /bin/pwd negates most of the
value I saw in using the simpler strategy.

I haven't found cases where "cd -P" is more correct.  Are there other
reasons to bother with "cd -P" at all?  Maybe performance: "cd -P"
would save a fork, which seems to make it ~10x faster.  Dropping buffer
caches doesn't seem to widen or narrow the gap, so I don't think the
filesystem access is much different, performance-wise.  But I don't
expect this "cd" to be a performance bottleneck; most scripts that do
something repetitive can just start off in the work tree root to avoid
the issue.

Falling back to /bin/pwd would help compatibility if it were easy to
detect when "cd -P" failed.  But since its failure is hypothetical for
me at this point -- I don't know of an environment where it fails -- I'm
not sure whether to expect it to fail with non-zero exit status or by
silently ignoring the "-P".  And to handle the cases of silently
ignoring the "-P" I'd guess cd_to_toplevel would have to run /bin/pwd
just to check that it ended up in the right place, which seems
counterproductive to me.  Do you think it would be reasonable to just
assume "cd -P" will exit non-zero if "cd" doesn't understand "-P", send
its stderr to /dev/null, and try again using /bin/pwd?

Marcel